Field of the Invention
The present invention relates to a magnetic sensor for detecting change in magnetic flux crossing a magnet-sensing plane caused by rotating a magnet.
FIG. 1 is a cross-sectional view showing one conventional magnetic sensor. The conventional magnetic sensor is provided with a resin frame 1 of the sensor, a rotating shaft 2 mounted rotatably in the frame 1, an arm 3 fixed to one end of the rotating shaft 2, a magnet 4 secured onto the other end of the rotating shaft 2 by an adhesion 5, and a ferromagnetic resistive element hereinafter merely referred as MR element) 6. The MR element may be formed of a glass substrate, a magnet-sensitive plane 6a constituted by a magnetic resistive pattern of NiFe as the ferromagnetic resistive material and formed on the glass substrate, so that the MR element is molded by an insulating resin to form a rectangular solid having a terminal 6b at a side thereof for input/output signal.
The magnetic sensor is further provided with a ceramic substrate 7 performing as a circuit substrate on which a pattern of electric wiring is formed and various kinds of electronic devices are mounted although they are not shown in the figure. The MR element 6 is mounted on the substrate 7 in such a manner that the magnet-sensitive plane 6a is parallel to the surface of the substrate, and the terminal 6b is soldered to the electric wiring pattern. In this state, the ceramic substrate 7 is accommodated and held in the resin frame 1 in such a manner that the surface of the substrate 7 is perpendicular to the magnet 4, that is, the magnet-sensitive plane 6a is perpendicular to the magnet 4.
The substrate 7 on which the MR element 6 is mounted is housed in a copper casing 8 acting as an electromagnetic shielding casing. The MR element 6 is connected to an input/output terminal 9 through a penetrating capacitor 10 for taking an output signal of the MR element 6.
The operation of the conventional magnetic sensor will now be described hereinbelow.
When the arm 3 rotates in association with the opening/closing condition of a throttle valve (not shown) disposed in an intake conduit performing as an air-flow path of a vehicle, for example, the rotation of the arm 3 is transmitted to the magnet 4 through the rotating shaft 2, that is, the magnet 4 rotates in association with the arm 3.
By the rotation of the magnet 4, the magnetic flux generated from the magnet 4 and crossing the magnet-sensitive plane 6 varies and, as a result, the resistance value of the magnetic resistive pattern of the MR element 6 varies in accordance with the variation of the magnetic flux crossing the magnet-sensitive plane 6a. The MR element 6 outputs the voltage corresponding to the rotational angle of the magnet 4.
The output voltage of the MR element 6 is amplified and then output through the input/output terminal 9 to the outside devices (not shown), and the opening/closing condition of the throttle valve is thus detected.
As described above, the conventional magnetic sensor may be employed as, for example, a position sensor mounted on a vehicle.
Since the detecting operation of the MR element 6 is based on the variation of the magnetic flux crossing the magnet-sensitive plane 6a as disclosed above, the positional relationship of the magnet 4 and the magnet-sensitive plane 6a strictly influences the characteristics of the magnetic sensitivity of the MR element 6. According to the conventional magnetic sensor, it is necessary to use an extra accurate positioning device for positioning the MR element 6 with respect to the ceramic substrate 7 and then the terminal 6b of the MR element 6 is soldered to the wiring pattern formed on the substrate 7 and, further, the ceramic substrate 7 is accurately housed in the resin frame 1 with reference to an outer diameter of the substrate 7 to keep a positional accuracy of the magnet 4 and the magnet-sensitive plane 6a.
FIG. 2 is a partial sectional view showing another type of conventional magnetic sensor, FIG. 3 is a cross sectional view cut out along the line III--III of FIG. 2, and FIGS. 4 and 5 are plane and side views schematically showing essential portions of FIG. 2.
The conventional magnetic sensor shown in FIGS. 2-5 is provided with a resin frame 101 of the sensor, a magnet 102 rotatably mounted in the frame 101, and a ferromagnetic resistive element (hereinafter merely referred as MR element) 103. The MR element 103 may be formed of a glass substrate a magnet-sensitive plane 103a constituted by a magnetic resistive pattern of NiFe as the ferromagnetic resistive material and formed on the glass substrate, so that the MR element is molded by an insulating resin to form a rectangular solid having a terminal 103b at a side thereof for input/output signal.
The magnetic sensor is further provided with a ceramic substrate 104 performing as a circuit substrate. The MR element 103 is mounted on the substrate 104 in such a manner that the magnet-sensitive plane 103a is parallel to the plane of the substrate. In this state, the ceramic substrate 104 is accommodated and held in the resin frame 101 in such a manner that the plane of the substrate 104 is perpendicular to the magnet 102, that is, the magnet-sensitive plane 103a is perpendicular to the magnet 102. Although it is not shown in the figures, a pattern of electric wiring is formed on and various kinds of electronic devices are mounted on the ceramic substrate 104.
The operation of the conventional magnetic sensor will now be described hereinbelow.
When the magnet 102 rotates in the direction A shown in FIG. 4 in association with the opening/closing condition of a throttle valve (not shown) disposed in an intake conduit performing as an air-flow path of a vehicle, for example, the magnetic flux generated from the magnet 102 and crossing the magnet-sensitive plane 103a varies and as a result, the resistance value of the magnetic resistive pattern of the MR element 103 varies in accordance with the variation of the magnetic flux crossing the magnet-sensitive plane 103a. The MR element 103 outputs the voltage corresponding to the rotational angle of the magnet 102.
The output voltage of the MR element 103 is amplified and then output through the input/output terminal 106 to the outside devices (not shown), and the opening/closing condition of the throttle valve is thus detected.
As described above, the conventional magnetic sensor may be employed as, for example, a position sensor mounted on a vehicle.
Since the positional relationship of the magnet 102 and the magnet-sensitive plane 103a directing along the arrow B shown in FIG. 4 strictly influences the characteristics of the magnetic sensitivity of the MR element 103, according to the conventional magnetic sensor, it is necessary to use an extra accurate positioning device for positioning the MR element 103 with respect to the ceramic substrate 104 and then the terminal 103b of the MR element 103 is soldered to the wiring pattern formed on the substrate 104 and, further, the ceramic substrate 104 is accurately housed in the resin frame 101 with reference to an outer diameter of the substrate 104 to keep a positional accuracy of the magnet 102 and the magnet-sensitive plane 103a in the direction B shown in FIG. 4.
The conventional magnetic sensors as disclosed above suffer from a problem that the longitudinal length of the sensor is increased since the MR element is mounted onto the ceramic substrate so that the magnet-sensitive plane is parallel to the substrate plane and the magnet is perpendicular to the substrate plane.
Further, since the terminal is soldered to the wiring pattern formed on the ceramic substrate and then the substrate is housed in the resin frame with reference to the outer diameter of the substrate, it is required to shape the outer diameter of the substrate with high accuracy and to keep high positional accuracy of the magnet and the magnet-sensitive plane with a high accurate positioning device.
Further, since the conventional magnetic device is provided with the copper casing covering the ceramic substrate for shielding undesirable electro-magnetic wave from the outside to prevent any error operation of the circuit, the assembling steps increase and the actual manufacturing operation becomes complicated.
Furthermore, since the magnet which is previously magnetized is manually fixed to the other end of the rotating shaft by an adhesion so that the magnetic direction of the magnet is arranged in a predetermined direction according to the conventional magnetic sensor, the distance between the magnet and the MR element may vary due to the rotation of the rotating shaft. Therefore, it is difficult to obtain the coincidence of the center point of the magnet to the center point of rotation of the rotating shaft and, further, it is difficult to obtain the magnetic direction and the positional angle of the arm with high accuracy.